Machine for producing convex surfaces



July 2, 1946.

L T. BOLAS ETAL MACHNE FOR PRODUCING CONVEX SRFACES Filed May 50, 1944 4 Sheets-snee: 2

July 2, *1946. J. T. BoLAs ET AL 2,403Q168 l MACHNE FOR PRODUCING )CONVEX SURFACES- Filed May 50, 1944 4 Sheets-Shee't 3 figg/a.

megus- @fz @1 M 53 July 2, 1946. J. T. BQLAS E TAL 2,403,168

MACHINE FOR PRODUCIQ: CONVEVX SURFACES I 4 sheets-sheet 4 5 s www i MTP? wwf.

` Filed May 50, 1944 Arr);

Patented July 2, 1946 MACHINE FOR PRODUCING CONV EX SURFACES John Thomas Bolas, Raymond William Edwards,

and William Joseph Latt signors to The Bristol Ae Bristol, England, a British company ited.

y, Bristol, England, as-l roplane Company Lim- Application May 30, 1944, Serial N0. 538,024 In Great Britain May 25, 1943 8 Claims, 1 This invention concerns machines for producing surfaces which are of convex Aoutline when viewed in one plane and which extend ina direction substantially normal to said plane. The latter extension of the convex surface is .hereinafter referred to as being in the direction of the long axis of said surface. I v

As examples of such convex surfaces mention is made firstly of theconvex radial surface which commonly extends along an edge smoothly to blend the surfaces meeting at said edge, and secondly of a ridge on a surface, the -ridge beingof semi-circular, elliptical, parabolic orother con- Vex outline in cross-section and extending'linearly or arcuately oversaid surface (thatiis along the long axis of the convex surface).

I Heretofore a common method of producing such convex surfaces has consisted of moving a profiled rotary cutter of concave formf for ex.- ample a, milling cutter) along a, linear or arcuate path With the plane of rotation of the cutter respectively parallel or tangential to said path. Since the cutter in producingsaid surface is moving along the long'axis of the curved sur# face and since in its direction of advance the cutter extends beyond that point to which the sur,- face has been formed, it follows that this method is precluded when it is desired to form said curved surface right up to-a face againstwhich the curved surface abuts. Y

It is an object of the present invention toprovide a machine which Will enable lconvexrvfsurfaces to be produced in the circumstances referred to above. l v, y u

It is a further object of the invention lto pro,-

vide a machine Whichwill form a convex surface Y under the circumstances referred to and which will at the `.same time blend said surface into the face which abuts said surface. y l ,Y According toy the present invention a machine 2( vex surface in a series of steps each of which is performed in timed relationship with the move-A Ament of the cutter across said surface and Awhilst the cutter is in non-cutting relationship with the surface; l A

It is preferred that an Q'Scillation of the cut.E ter in one direction corresponds to a cutting stroke whilst an oscillation of the cutter in the opposite direction corresponds toa return stroke ofthe cutter, the arrangement being that when the cutter has completed its return' strokey it automatically effects a feed movement Hume diately followed by a cutting stroke. i A

A specific embodiment of the invention as ap= plied to a machine for forming. a convex surface on an impeller for a centrifugal supercharger Will now be described merely by Way of example with reference to the drawings accompanying ythis specification in which: l

Figure v1 is a View .of part of a doublefshrouded impeller for a centrifugal supercharger, .the view being taken in a .direction facing theeyeof ,the

impeller and the .from/shroud,

Figure 2 is a section .on the line II'1I. of rig# ure 1,

Figures 3a and 3b together forma diagrammatic layout of a machine f0.1' performing 4certain. operations on the i-mpeller shovvnin kFigures@ and 2, `and Figure 4 is aplan view of part of the showing the mounting for the impeller.

It is clear from .Figures 1 and 2 that the im-v peller 4 comprises a frontshroud a, a backshroud for producing a surface 'of the form referred rto is characterised in'that said'surface is produced by a tool which is reciprocated relatively to the Work in a plane normal to the direction in which said surface extends and which is. moved in said directioin y y According to another feature of the presentinvention a :machine for forming a convex surface along an edge of a Work-piece is characterised in that said surface is produced by a cutter which is oscillatedrin a plane normal yto the direction in which ,said edge. extends about an axis coincidental withl the centre of curvature V.of the con- Vex surface and which is vfed along said edge.v

VAPreferably thewcutter is movedvv along the conb and a plurality of equi-spaced radial-blades e extending .between the shrouds and from theeve of the impeller d to the periphery e thereof. l

In order that such an impeller may bebal.; anced at the high speeds for which it is-designed to operate and is aslight as .-is possible thefaces shown in full lines in Figure 2 are fully machined. That portion of theinner face .of the front shroud a shown at fhas .commonlyheen produced .by hand Work because' ofthe diiliculty of machining this face.4 It vis nowbelieved .that certain outf'of balance forces which areset up at. highaspeeds of rotation of the impeuer are .dueitothis hand workingsince the'amount of metalremovedfatf machine shown diagrammatically in Figures 3.a'

` and 3b has been evolved.

kThis machine .must producev a convex surface f which terminates atboth'e'nds inlbladesvciahd vvhichis blended as at 01 .and g2.'intlrsaidY blades,

3 Moreover the surface f is arcuate, the radial centre of which is coincidental with the centre of the impeller. t

` In View of the diiiculties referred to hereinbefore of moving aproledconcave tool along face when the .latter must blend into blades yc'the machine incorporates an oscillating cutter .5

and produces the desired convex surface f. The

cutter is withdrawn from the impeller eye during the return stroke.

such return stroke the impeller as a whole is fed f around centre h by a small amount 'and another .l

cutting stroke is then begun. The cutting thus proceeds until the cutter (whichcommenced machining at g1) reaches g2 whereupon the cutter is withdrawn from this` pocket and the impeller is brought to a new indexing position to enable thecutter to operate on the face f associated with the next adjacent pocket ofY the impeller eye.

I t will have been noted that reference hasbeen .made to the centre of arcuate facefbeing at h and to the feed movement taking place about axis z'. This impellery 4 (see Figure 3a) 'is lmounted upon a Vplate 1 carried by atab1e'18 which is pivotally mounted'at 9. The v table` 8 is capable of 'rotation'about axis i to enable the indexing operation to be performed, and plate 1 is carried on thetable so as4 to be movable therewith. The, table has acarn face 8 whch enlgages witha stationary roller 8" so that as the `table is rotated it is also reciprocated, The plate 11therefore hasiinparted to it acompound move-` ment which ensures thatv as the cutter performs `itscutting operation, face f will have the contour 1d esired: thatis it will'be 'an arc of centre h.

To enable the impeller 4 to be placed upon `plate 1V prior tothe'machining operation corn- ;mencing, to` enable the indexing operation to beV lperformed, and to enable the impeller to be re- `moved afterthe. operation has been completed, I table 8 is lowered away from Vthe cutter. l angtherimpeller is mounted on plate 1 and when anY indexing operation has been completed the 1 table is raised to bringthe impeller to the cutting position. f'

g When Oil under. pressure frointhe constant delivery Q pump I passes to a twin-pressure valve Il and thento the various" circuits either as high-pres- 3 sure or low-pressure oil. Injligures Y3a and 3b the higlfr-pressure oil circuit" is shown ras ia x dotted line, `the low-pressure oil Vcircuit as a chain dotted line andthe exhaust circuit as a l double line.

` Low-pressure oil from valveVV I'I passes by pipe I2 to the valve I3 which controls the indexing and table positioning operations. The latter are I2 which is directed to the bottom of the valve 2,403,168 "f pfff thereby set to permit low-pressure oil to pass :to cylinder r15,1;(YWe1' the table 3.1'

'- In- Ithe event that the'indexing is1 incorrectly l performed the plunger I8 will engage the underwhich is pivotally mounted at 5 (Figure 2'). This face of the indexing plate |04, and will thereby cutter enters a pocket of the impeller eye dto Y perform its cutting stroke. Upon the cuiavter'erify Y gaging the shroud a it shaves metal therefrom be prevented from moving upwardly in cylinder |4. Accordingly the low-pressure oil from pipe |9 is incapable of raising the latter since it abuts on the completion of each vented from passing to cylinder |5 to raise the table.. When-correct indexing is performed valve plunger I8.v The valve I9 is thus maintained in its lower position in which pressure oil is pre- |9` is free to'be raised to permit the pressure oil to pass to the cylinder I5 to enable table 8 to be raised to the cutting position.

It is necessary'to ensure that the cutting operation cannot be commenced unless the table 8 is in its fully raised position. This is provided for by a plate 20 which is associated with the table and which is raised and lowered therewith. The `plate 2|! has a pairof'notches; notch l2| corresponding to the fully raised table position.

. and notch- 22 the fully lowered position.

ation. At any 'position inter-mediate notches 2| and 22 the plunger 23 abuts plate 20 and pre'-r vents valve 24 opening;

As already stated the'cutter 5 is pivotallyA mounted at 6 (Figure 2) andis: oscillated into and out of each'pocketof the impeller eye d. The cutter isofl crescent-shape and is carried by'cutte'r shaft 25. The'latter also carries the y vane 26 of -ahydraulic vane motor 21, the arrangement being that upon pressure oil passing to one side of vane 2S it moves the cutter in one performed respectively by ran indexingjcylinder I4 anda positioning cylinder I5. The passage'of f ressure oil to these two cylinders` is .brought depressed, piston-valve |1fis` raisedy and conse- A is thus locked in eachL indexingjposition before the .table is raised.

valve'll assumes'itslower position'and'pressure J To withdraw the indexing plunger '|'8j and'lower the table. 8, "hand control I 6 jis raised.;H jPiston-f "rection and upon the pressure voil passing to the other side of vane' 21 the cutter is moved'in thevopposite direction.

Y' Associated with the cutter is a ring 28 which carries internal teeth 29 and external teeth 3|).Y

Engaging teethy 29 is a pawl 3| and engaging teeth 30 is a checkpawl 32;. It is to' be noted thatv although in Figure 3d, pawl 3| is shown as passing through shaft 25 nevertheless in actual practice theconnection isV througha gear train which ensures that vfor each single oscillation thev pawl moves through an arc corresponding to slightly over theA width of -oneof teeth 29.

Thus when pressure oil enters the Vanev motor 21 and turns lthe cutter shaftf25 anti-'clockwise tol-,perform the cutting stroke, pawlv 3|'. slides over one of teeth 29. .Pawl 32 remains in" engagement with teeth 33 land lprevents anticlockwise rotation of the ring 23. Said-antil clockwiseV rotation ofA Vring 28 is efe'cte'dri'ibya springwhich is not shown. Onthe return'fstrole of the cutter (which isfproducedbyV vane motor 21'moving the cutter shaft-clockwise), pawl 3| engages one of teeth '29'vand rotates the ring Y28 in a clockwisedirection through thewidth of one ofsaidteeth.' v Y Y t Each such movement'of the :ring r28 corref sponds with"v each feed movement' and.'Y when i the when the feed is just started. The final position f of hole 33 in relation to plunger 34 corresponds to the end of the cutting'operation when the feed movement is completed.

The plunger 34 is urged during the cutting operation towards the left, i. e. against ring 28.

Whilst the plunger. 34 abuts thering 28 pressure' oil passes to the vanemotor`21 andto the feed mechanism through a master control valve 35 with which the plunger is associated. When hole 33 is brought under plunger 34 it drops 'therein and valve 35 is set tostop the flow of pressure oil to the cutter and feedmechanisms.

It is clear therefore that when the cutter has completed its production of face f 'and has reached edge g2 the cutter and feed mechanism are rendered inoperative. Since each movement of ring 23 to move hole V33 towards rplunger 34 occurs only during the return stroke of the cutter it follows that'the plunger can only engage hole 33 to stop the cutter'and feed opera-tion during the last return stroke of the cutter i. e. only when the latter has 'been raised clear of the work.

The plate 1 is intermittently turned at the end of eachv return stroke of the cutter as will now be described. v l

Over a pa'rt of the'periphery of plate 1 there are provided ratchet teeth 3S which are engageable by a pawl 38 and a check pawl 31. AIThe pawls 31, 38 are normally held in engagement with the teeth by the pressure of a spring 39 located within cylinder 40. The'piston rod in the latter carries pawl 31 and has an extension'4l to-engage pawl 38.

` vEach time the cutterreaches fthe limit of its return stroke, pressure oil passes to the bottom of cylinder 42 (as more fully described hereinafter) to raise pawl 38 and thereby effect the feed movement of plate 1. Each time 'the cutter reaches the limit of its cutting stroke pressure oil passes to the top of cylinder 42 and pawl 38 is moved downwardly ready for the next feed movement. .Check pawl 31 maintains plate 1 against rotation. i

When the cutting and feed operations have been completed pressure oilpasses'to cylinder 40 to move it against the' pressure of springl 33 and thereby withdraw pawls 31., 38 from teeth 36. Hydraulic motor 43 (against the lower face` of which low pressure oil is always maintainedlis then free to rotate plate 1 in an anti-clockwise direction to its starting position.

This intermittent feed movement of plate 1 is supplementary to the indexing movement whose action has already been described. Briefly the two movements may be considered to be an indexing movement to bring edge g1 rapidly under the cutter followed by ar series -of `intermittent stepsfwhichfeed the work along under the cutter. When the intermittent feed movement has brought edge g2 under the cutter it stops and is followed by an indexing movement to bring edge.

anca-:res

which are used to effect the operation This now' follows. v

The start-and-stop manual control comprises a pilot valve 44A which is capable of endwise movement to control the passage of low-pressure fluid from pipe 45 to the master control valve '35 by way of pipes V46, 41. I f

To start the cutter operationV (assuming.y that of these.

, the table is in the fully raised position and plunger 23 liesopposite notch 2i) pilot Valve 44 is drawnv effect of raising plunger 34 outof hole 33 and moving the valve to the extreme right-hand .posia tion. It will be noted that in this position oil may drain from the right-hand side by'pipe 45 and valve 44. i

High pressure oil from pipe 49 passes through the automatic stop-start valve 58 and pipe 5I to valve Z4. This is pushed to the left by the 'highpressure oil and plunger 23 enters notch 2 i; Consequently the high-pressure oil is enabled toflow by pipe 52 to master valve 35 Iand*thelatter-per mits. the oil to passV by pipe 148 to an automatic reverse valve mechanism generallyllindicated at 53. From the latter itflows by eitherfpipef54'or 55 to the vane motor 21of the-cutter. j Y y In the position of the various valves just yde-A scribed the cutter is. in operation but the feed mechanism is not since the-feed vcylinder-`42 is cut-off fromV its source of high-.pressure oil by master valve 35. l" f* of valve 35 The movementof the master valveto the to the left until plunger 34 abuts ring zfand pawl 32 is brought into engagement' with teeth 30. The master Valve -is rthen in a'position to `permit high-pressure oil from .pipe 52 to conti-nue to pass by pipe 48 to the automatic reverse-valve mechanism 53 and thence to` vane motor'21'1n its new position however valve -35 also-permits the high-pressure fluid from valve mechanism 53 to pass by pipes 14, 15 to the feed vlinder 42 so that the latter is operational.

The cutter and feed mechanism are nowwboth in operation and the various parts of the lmachine are somewhat in the condition shown-in Figures 3a and 3b. l 'I As has been stated previously the cutterfand 'feed operation are interconnected. This is done through the medium of the automatic reverse mechanism 53. Y #-17 The high pressure oil for performing the 'cutting andfeed operations derive from ,pipe 56 (and the master valve 35) and is directed to eachmechal nisrnto produce the desired function in the desired sequence by mechanism 53. I f

Mechanism 53 comprises two main parts: `one associated with the cutter and the other with the feed operation.r Both main parts are similar in construction. Thus associated with the cute ter mechanism there is 'a pilot valve 51, a reverse valve 58, and a pair of change-over valves 53,33'. Similarly associated with the' feed mechanisinisa pilot'valve Si, a reverse valve 621anda pair' of change-over valves 63, 64.

Y The high-pressure oilalso' passes by pipe 10 to change-over valve 63. This valve is maintained in the position shown in Figure 3b 1by the low-pressure fluid.

l beisummarized Vasfollows:

L7 y i Each'of the .change-over valves is normally maintained by low-pressure oilfrom pipe65,v 66 in a position at which both ends. of -eachY pilot valve 51, 6| "are connected to drain (see Figure 3b);Vv The pilot and associated v'reverse valve are connected by pipes as shown; The valve assembly 53 operates as follows: .High pressure oil from pipe 5| enters valve assembly 53 and is directed into branch pipes 61 and 68. The former is associated with the feed mechanism andthe latter with l'the cutter mechanism. A For the Acutter mechanism pilot valve 51 and reverse valve 58 are in their extreme right-hand position thus permitting the high pressure oil frompipe 68 'to pass through the pilot valve 51 and by pipe 69 to valve 58 which is thereby held inlthe right-hand position. Consequently highpressure oil is allowed to pass through valve 58 `and by pipe 54 to vane Ymotor 21.

from pipe 54 Forr the feed mechanism pilot valve 6 |v and re-V verse yvalve 6 2 are in'their eXtremeright-hand position. High pressure oil from pipe 61 is thus enabled to pass through the pilot valvel and by `pipes 1| to valve 62. The latter is therefore held in its right-hand position permitting high-pressure oil to pass through the valve, and by pipe 12, `to feed cylinder 42. `This state of affairs was brought into being when the cutter reached the Qlimit of itsv cutting stroke and has resulted in `pawl 38 being moved downward ready for the ;next feed movement. Y

The above state continues until the return `stroke of the cutter has been completed. When this happens vane 26 ,of Vmotor 21v will have irreached the limit of its clockwise movement and [is therefore restrained from further motion. Oil Y `from pump I0 continues to be delivered to the lhigh-pressure system, and the pressure therefore Y rises. 1 f

This increase of pressure onbeing transmitted 1togchange-over valve 63 opens it and the oil lpasses to the right-hand end of Vpilot valve 6|; `The latter is therefore moved to the left-hand whereupon high-pressure oil from pipe 61 is dilrected bypipe 13 to the'right-hand side of re- ;verse valve 62 whichr is thenV moved to the left and keptthere. V

High-pressure roil is thenfable to pass through valve 62 and by pipe 14. to'master valve 35 and then to feed cylinder 42 by pipe 15. Pawl 38 is `raised and table 1 rotated by one feed movej ment.

The high-pressure oil upon entering pipe V14 is carried by npipe 16 to changeover valve 59 which is therefore opened to allow the pressure oil to the right-hand side of pilot valve 51. When this l is moved to the left by the pressure oilit'directs g the latter through pipe 81` to the reverse valve 58 which is also moved to the left.` This permits high-pressureoil to pass through the valve and to pipe 55. The vane motor 21 is therefore moved anticlockwise and the cutter performs its cutting stroke. y Y

A'similar sequence of events is followed when the cutting stroke is completed andthe vane 26 l of motor 21 has reached the limit of its travel g in an Yanti-clockwise direction. These events'may (a)V the pressure in the hydraulic Vsystem is raised throughout. This increased pressure'on being transmitted through pipe 11to change-'over I ne'xt feed .movement transmitted to change-over valve 60 by pipe 18 and is accordingly opened.

(d) as a result of change-over valve 60 open.

ing pilot valve 51 and subsequently reverse Vvalve 58 move to their right-hand positions. l

(e) pressure oil-therefore passes to vane motor 21 by pipe 54 andthe cutter performs its return stroke. i v

At the conclusion of the latter the pressure build up produced the series of valve changes described above with the final result that the feed movement takes place and then the cutting stroke is begun.

The sequence of cutter strokes, valve changes, and feed movements details is followed until the condition shown in Figures 3a and 3b is reached. These ,figures show the positions of the various parts whilst the cutting and feedingV operations are effective Vwith the cutter performing its last return stroke.

From this positionv when vane 26 Areaches its extreme clockwise travel (that is the cutter has completed its last return stroke) -hole v33 is brought under plunger 34 (as already described in detail) and'valve 35 is movedby low-pressure oil towards the left so that the plungerfenters the hole. Y g Y Y The mastervalve 35 when in this position prevents the flow of high-pressure oil from pipe 52 to'pipe 48 and from pipe 14'to pipe 15. The cutterv and feed operation therefore ceases with the cutterwithdrawn from edge y2, thesurface f having'been produced. At the same time rvalve- 35 permits high-pressure oil toA pass vfrom pipe 52 to cylinder40 by pipe19. This withdraws the check and feed pawls 38 and 31 respectively andthe table 1 isereturned to its starting posi-r tion by Amotor 43 which isv continuously/supplied with low-pressure oil. y

The operator is then required to perform three control movements toindex the work for thek machining'ofthe next adjacent pocket of the impeller. ,l 1

YThe rst control movement is'to rotate the manual control valve 44 through 90 degrees in a clockwise direction from the position shown in Figure 3a.. It will be noted that this valve terminates in a rotary valve portion 88 (shown also in transversesection in Figure 30,) 'and that this rotationpermits low-pressure oil from pipe 45 to be directed by pipe 8| into a cutter interlock valve 82. -It is clear from Figure 3a. that this valve is onlyopen to the flow of pressure oil when the cutter is in the .fully retracted positionrelativefto the work. When this happens the ypressure oil flows from the'interlock valve bypipe 83 to the right-hand yside Vof a stop-start kvalve 50. The latter consequently moves'to the left' and highpressure oil is directed'from pipe 49 to pipe 85 andr then to valve 24; plunger 23 isy thus withdrawnfromnotchZl. 'f Y The second control movement is to actuate the indexing and positioning control' I6 to withdraw the indexing plunger i8 and'then'lower table 8.

-The third control movement is toactuate contro1-|6after indexing has .beenV performed r so The pressure oil is also,k

4that the table 8 is raised and the indexingv plunger I8 advancedito Iitslocklng position.

The second and third control movement have been described` in detail'above.

Manual control 44 is then rotated'through 90 voperation as already described. The operator then pushes valve 44 to its extreme left-hand side position and this brings the feed mechanism into operation.

Finally in the event that during machining the operator wishes to stop the machine he will rotate the manual control 44 and hence the rotary valve 80 to enable pressure oil to pass to the interlock va1ve'82 and the stop-start valve 53 with the-results already indicated. The machine is automatically brought to a standstill only when the cutter has completed the first return stroke after actuation of control 44since it is only when this has happened that valve 82 is open for the passage of pressure oil to the stop-start valve 5i).

In an alternative construction (not shown) in which a crescent-shaped grinder replaces the cutter the feed mechanism is operated continuously so that grinding occurs during the cutting and return strokes referred to above.

To enable this to be done the pilot, reverse and change-over valves 6I, 62, 63 and 64 respectively of valve mechanism 53 which are associated with the feed mechanism are dispensed with. The feed plate 'I is continuously rotated in one direction by an electric motor which is started and stopped by a hydraulically actuated switch. To operate the latter, pipe 45 is connected to pipe 14 so that low-pressure oil frompipe 45 enters the master valve 35 by pipe'14 and is capable of being directed therefrom into pipe 15 which leads to the hydraulically actuated switch. It is to be noted that these two pipes (14 and 15) are placed in communication with each other through master valve 35 only when the cutter has commenced operating. When the latter stops (the surface f having been produced) the master valve 35 assumes a position which stops the flow of pressure oil to the hydraulically actuated switch and it thereupon opens to stop the electric feed motor.

I claim:

l. A machine tool comprising a cutter mounted to oscillate about one axis and perform cutting and non-cutting strokes alternately, a work-support mounted to turn relatively to the cutter about a second axis transverse to and spaced from the first axis, a fluid motor connected to the cutter to oscillate it about the first axis, feeding means for turning the work-support, relatively to the cutter, about the second axis step by step in one direction, a second fluid motor connected to the feed means to actuate it to effect one step of turning movement, a source of fluid under pressure, valve means actuated by the cutter motor at the end of each non-cutting stroke of the cutter to admit fluid from said source to the second motor second'r axis spaced yfrom and transverse` to the 'first axis, steppingmeans for turningthe worksupportl aboutthe second axis step 'by'ste'p, a reversible fluid motor connected to the stepping means to actuate it to effect one step of move- 'ment when the motor makes a feed stroke in one direction and to reset the stepping means when the motor makes a return stroke in the other direc'tion, a source of fluid under pressure, and valve means actuated by the means for oscillating the cutter to admit fluid from the source to the motor tocau'se it to make a feed stroke when the cutter reaches the end ofeach return stroke and to admit fluid to themot'or to cause it to make a returnr stroke when the cutterreaches the end of each cutting stroke.

'3. A machine tool comprising a cutter mounted to oscillate about one axis through cutting and return strokes alternately, a reversible fluid motor to actuate it to turn the work-support relatively connected to the cutter to-rock it about said axis in one or the other direction depending on the direction of action'of the motor, -a work-support mounted to turn about a second axis transverse to and spaced from the first axis, feeding means for turning the work-support about the second axis step by step, a second reversible fluid motor connected to the feeding means to actuate it to feed the work-support or reset it depending on the direction'of action of the motor, a source of fluid under pressure, and valve means which connect the source to the motors and is operable cyclically to reverse the connections to each motor alternately to make the first motor make a cutting stroke, the second motor a reset stroke, the first motor a return stroke and the second motor a feed stroke in sequence.

4.. A machine tool according to claim'B, wherein the valve means comprises two reversing valves in the connections from the source of fluid to the fluid motors respectively and operable each to reverse the direction of action of the associated motor, and separate actuating means for each reversing valve which means is subjected to the fluid pressure in the motor associated with the other reversing valve to be actuated thereby to reverse the setting of its reversing valve and, in opposition to said pressure, to a load which maintains the actuating means inoperative until said fluid pressure rises above a normal value on the motor reaching either end of its stroke.

5..A machine tool according to claim 2, comprising also a device movable step by step from an initial position to one in which it stops further operation of the machine, means actuated by the *power means for oscillating the cutter to move said device one step during each return stroke of the cutter, means for restarting the machine, and means for resetting said device to its initial position When the machine is restarted.

6. A machine tool according to claim 3, comprising also a master valve controlling the supply of fluid from the source to the motors, a device operative to adjust said valve to provide a supply of fluid to the motors and movable step by step to a position in which it adjusts the valve to interrupt the supply yof fluid to the motors to stopv Viiuid to -themotors; an .valve open against the bias on it to` provide a supabutment holding the said plyvsof uid tothe motors Yand adjustable step by vstep froman initial position to one-'in Which it releases said valve which thereupon closes to stop the machine, means operable by the motor for y'the cutter to advance theabutment one step dur-v yling' each return stroke of the cutter and means for .resetting the abutment toiitsfinitial position when the machine is restarted.

8. A machine tool comprising a cutter'mounted to oscillate and perform cutting and return strokesv alternately, a uid motor connected to thevcutter ,to oscillate it, Va Work-support mounted to turn Labout a second axis normal to and spaced from the rst axis and also mounted to move from a normal position away from the cutter to allow of a work-piece being mounted on it, means forv stepping the Work-support in one direction about the second axis, a second fluid motor arranged to actuate the stepping means, a source of iluid under pressure, valve means connecting the moy.tors to the sourceof fluid and .operable automatically to change the connections in sequence fto adjust ythe motors to operate the cutter through a cutting and return stroke followed by a step 'of movement of the Work-support in sequence, a master valve controlling the supply of Iluid from the source to the motors, means adjusting the r master valve to provide a supply of fluid to the motors and operable by the motor Yfor the cutter during the last of a' predetermined number, of return stokes of the cutter to adjust the master valve to interrupt the supply of iluid to the motors. and stop the machine, means for restarting the machine, and a locking valve normally permitting uid from ,the source to pass through the master valve to the motors but operable byr vthe Work-support when it is moved away from the cutter from its normal positionto interrupt the passage of fluid through the master valve. Y

JOHN THOMAS BOLAS. RAYMOND WILLIAM EDWARDS. WILLIAM JOSEPH LATTY. 

